As a mobile communication technique in a cellar system, a sector transmission and reception method, in which a base station has a plurality of base station antennas composed of directive antennas and each of a plurality of cells comprises a plurality of sectors where a different frequency is used for each sector to communicate, has been developed.
The sector transmission and reception method allows to use the same frequency repeatedly in nearer cells, which makes the efficiency of frequency reuse higher and increases the number of users accommodated.
In the sector transmission and reception method described above, when a mobile station in communication moves from a cell to another cell, a handover between cells by a switching equipment is executed. And when a mobile station cross a boundary between sectors, a handover between sectors by controlling of a base station is executed.
For instance, In Japanese Unexamined Patent publication No.7-131845, a base station apparatus for executing sector-transmitting-receiving is described. The base station apparatus is to execute data communication on the basis of CDMA (Code Division Multiple Access) mobile communication system. Illustrated in FIG. 6, the base station apparatus described above comprises M numbers (M is an integer number indicating the number of cells) of sector antenna 303, M numbers of batch modulating/demodulating section 302-1 through 302-M to modulate and demodulate transmission and reception signals by a plurality of communication channels in the batch in a frequency determined for each sector and N numbers (N is an integer number indicating the numbers of communication channels) of baseband signal processing section 301-1 though 301-N to process baseband signals of each communication channel. In addition, in FIG. 6, CLK illustrates a clock signal to operate each circuit.
As illustrated in FIG. 7, each of baseband signal processing section 301-1 through 301-N comprises transmission signal processing section 201 to generate transmission signal Sn corresponding to a modulation method from transmission data SDn, transmission signal selecting circuit 202 to output this transmission data Sn to the instructed sector, reception signal selecting circuit 204 to select signal RAm(m=1.about.M) received by each sector according to an instruction, reception signal selecting processing section 203 to detect reception data RDn corresponding to the communication channel from selected reception signal Rn, monitor signal selecting circuit 206 to select signal Am received at each sector according to an instruction to output, reception quality monitoring section 205 to monitor the reception quality of the reception signal selected by monitor signal selecting circuit 206, and control section 207 to instruct monitor signal selecting circuit 206 to switch a sector to be selected at a certain time intervals, and to instruct transmission signal selecting circuit 202 and reception signal selecting circuit 204 to select a sector having the most appreciate reception quality on the basis of the detection result by reception quality monitoring section 205.
In the base station transmitting and receiving apparatus, transmission data SDn (n=1.about.N) of the number n channel is input to transmission signal processing section 201 at the number n of baseband signal processing section 301-n. Transmission signal processing section 201 generates transmission signal Sn corresponding to a modulation method from this transmission data SDn. This transmission signal Sn is input into transmission signal selecting circuit 202. Transmission signal selecting circuit 202 outputs this transmission signal Sn [Sn,m=Sn(m=SEL1), Sn,m=0(m.noteq.SEL1)] to a sector instructed by selecting signal SEL1 from control section 207. In addition, Sn is a waveform indicated in digital signals.
Transmission signal Sn,m output from transmission signal selecting section 202 of signal processing section 301-n is input to batch modulating/demodulating section 302-1 through 302-M. Batch modulating/demodulating section 302-m add transmission signal from S1,m to SN,m provided respectively from baseband signal processing section from 301-1 to 301-N, converts them into analog signals, then converts into transmission radio signals. This transmission radio signals are transmitted from antenna 303 at a sector. Signal RFm (m-1.about.M) indicates transmission and reception radio signals of the number m sector.
On the other hand, signals received by antenna 303 of each sector is input into batch modulating/demodulating section 302-1 through 302-M. Batch modulating/demodulating section 302-m converts reception radio signals in a band corresponding to N numbers of communication channels into baseband signals collectively then converts them into digital signals to output. This baseband signal RAm is provided to all of baseband signal processing section 301-1 through 301-N.
Reception signal selecting circuit 204 at baseband signal processing section 301-n selects reception signal Rn [Rn=RAm(m=SEL1)] of the sector instructed by selecting signal SEL1 at control section 207 from M numbers of reception signals RA1 through RAM to output into reception signal processing section 203. Reception signal processing section 203 detects reception data RDn corresponding to the communication channel from the selected reception signal Rn.
And, control section 207 switches selecting signal SEL2 for monitor signal selecting circuit 206 at intervals of predetermined duration time. Monitor signal selecting circuit 206 receives it, selects reception signal RQn [RQn=RAm (m=SEL2)] of the sector instructed by selecting signal SEL2 from M numbers of reception signals from RA1 to RAM to output into reception quality monitoring section 205. Reception quality monitoring section 205 monitors the reception quality of the selected reception signal RQn (for instance, reception power, interference wave power, examination error power, error ratio and others) to transmit to control section 207 with reception quality signal Qn. As described above, control section 207 monitors the reception quality of each sector by using reception quality monitoring section 205 and outputs selecting signal SELL to select the sector having the best reception quality into transmission signal selecting circuit 202 and reception signal selecting circuit 204.
Accordingly, when a mobile station moves crossing a sector, the most appropriate sector is selected automatically within baseband signal processing section 301-1 through 301-N.
As described above, in a conventional base station apparatus in a mobile communication, when a mobile station moves crossing a sector, a handover controlled by the base station, where the base station decides the most appropriate sector on the basis of reception signals received from a mobile station, is executed.
And, since a handover in a conventional base station apparatus is controlled by the base station where a basebnad processing section selects the sector having the best reception quality on the basis of reception quality signals from each sector, there has been a problem that a scale of hardware becomes larger because a comparing circuit is necessary to detect the reception quality from each sector and select a sector on the basis of the detected qualities.
And, since a handover is executed by a hard handover in which a connection with a cannel is once terminated to switch a channel for a new connection with another channel, there has been a problem that generated short break brings deterioration in reception quality.
And, since a transmission from a base station is executed through one line, there has been a problem that a soft handover, in which reception signals from a plurality of sectors are composed for handover, can not be executed.